It is well-established that exposure to high fluoride levels during early childhood increases risk of Dental fluorosis. Evidence in mice strongly suggests that inherited genetic variation is also important. Both animal models and analyses of human twins provide strong evidence that risk of Dental caries is also highly heritable. To date, however, no human studies have evaluated the effect of individual genetic variation on fluoride biology or fluorosis risk. High-throughput assays for Single Nucleotide Polymorphisms (SNPs) have greatly enhanced the ability to identify genes for complex traits such as Dental fluorosis. Investigators can analyze over 500,000 SNPs distributed throughout the genome quickly and at reasonable cost. Since these phenotypes involve multiple genes and interactions with environmental variables, large sample sizes are necessary to provide adequate statistical power. This study will evaluate 3,458 school children age 11-15 in a region of Ireland where most (but not all) drinking water is fluoridated. A total of 520 fluorosis cases and 605 controls will be recruited. DNA from saliva will be used for whole genome SNP association studies and fine mapping in regions with highest statistical significance and in high-priority candidate genes based on biological function (e.g., enamel proteins). Caries and fluoride exposure data will also be obtained. Fluoride exposure was previously obtained by our team 10 years ago for 125 of these subjects and the follow-up will allow assessment of the accuracy of retrospective parental reports. Both parents and one sibling for a nested set of 100 cases and 100 controls will be recruited and clinically and genetically evaluated, and a fluoride challenge study will be conducted on 100 of these parents (50 fluorosis affected and 50 unaffected) by measuring 24 hour urine excretion following a 3 mg oral fluoride dose. The primary pharmacogenetic Aim is to identify specific genes and variants that affect individual differences in risk of Dental fluorosis. Secondary Aims are to evaluate the extent that Dental fluorosis aggregates in families of fluorosis cases versus controls after accounting for variation in fluoride exposure;to assess whether 24 hour urine excretion rates of fluoride differ between fluorosis cases and controls and whether fluorosis susceptibility genes have an effect on excretion rates;to evaluate relationships between Dental fluorosis and caries in individuals and families;and to identify susceptibility genes for Dental caries.